Dynamometer excitation control system



June 6, 1944.

DYNA/10 1575? EXC/TA 770 R. H. KAUFMANN 2,350,766

DYNAMOMETER EXCITATION CONTROL SYSTEM Original Filed Sept. 4, 1940Richard H. Kaufm ahn His Attorney.

Patented June 6, 1944 2.850;! mmulomm IXII'I'ATION CONTROL 8Y8!!!liohardll.

rationorNewYork mm ,N.Y.,alllgnortofienerallleetriecolnpany nary z,104:, Serial No. 414,410

3 Claims. (01. ru -2:3)

'Ihisinventionrelatestoanelectricaldynamometer system and particularlyto an electrical dynamometer system which is adapted to imposealoadofcertaincharacteristicsuponapower source such as an internalcombustion engine.

An object of my invention is to provide an improved dynamometerexcitation control system.

Another object oi my invention is to provide an excitation controlsystem for a dynamometer employed for loading a mechanical power sourcewhereby the actual operating characteristics of the power source may beduplicated by causing the power absorbing means to have a definite andpredetermined relationship to its speed.

A further object of my invention is to provide an improved dynamometerexcitation control system in which the total dynamometer excitation isfunctionally related to the speed and which may have components whichvary as the first or second power of the speed or assume intermediatevalues of total excitation between these two limits.

Further objects and advantages of my invention will become apparent andmy invention will .be better understood from the following descriptionreferring to the accompanying drawing and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

In order to simulate in the laboratory the conditions of actual servicewith various types of loads, for example, propellers driven by aninternal combustion engine, it is desirable to provide an excitationsystem for a dynamometer employed in loading the prime mover or enginewhich automatically will maintain with varying loads the desiredpower-speed relationship. In carrying out my invention in its preferredform, a pair of direct current exciter generators which are driven at aspeed proportional to the dynamometer are adapted to be employed toprovide a component of excitation to the dynamometer. One of theseexciter generators has its armature connected to a field excitingwinding of the dynamometer while its field is provided by field excitingwindings connected in circuit with the armature of the other excitergenerator and with an adjustable voltage source of electrical powersupply. The other exciter may be excited either from an adjustablevoltage source of electrical power supply or by means of a permanentmagnet, the former being the preferred arrangement because oi itsflexibility and the ability to avoid excessive voltages. The excitergenerator whose armature is connected for supplying excitation to thedynamometer field is operated preferably in the unsaturated condition.The dynamometer power absorption may be made to vary automatically overa wide range as a function of speed by adjusting the relative magnitudeof the adjustable and variable components of excitation supplied to thefield of the exciter generator which supplies dynamometer fieldexcitation. Further, an additional controllable component oi excitationindependent of speed may be provided to the dynamometer by another fieldexciting winding. The response of the system can be improved and smallermachines driven by the dynamometer by connecting the dynamometer fieldto an electric amplifier which is controlled by the exciter generatorsdriven by the dynamometer.

In the drawing, Fig. 1 is a schematic electric circuit diagram ofapparatus arranged in accordance with my invention; and Fig. 2illustrates several characteristic curves which will be employed inexplaining my invention.

This application is a division of my copending application Serial No.355,321, filed September 4, i940, and assigned to the assignee of thisapplication. Referring to the drawing, I have shown a system for testinga prime mover II in the form of an internal combustion engine having athrottle Ii and mechanically connected by a shaft I2 to a rotor i3 of adynamometer of the inductor eddy current type. Connected also to theshaft I! or arranged to be driven at a speed proportional thereto arethe rotors or armatures I4 and ii of a pair of direct current excitergenerators. The dynamometer is provided with a field exciting winding itwhich is adapted to be excited by the exciter generators through anamplifier of the dynamo-electric type comprising a conventional directcurrent generator which is preferably designed to operate on thestraight portion of its saturation curve and which includes an armaturei1 and a field exciting winding II. The amplifier also includes asuitable constant speed motor is preferably of the synchronous orinduction type for driving the amplifier generator armature II. Sincethe direct current generator is operated in the unsaturated conditionand has its armature il driven at a constant speed, it delivers avoltage to the dynamometer field it which is proportional to theexcitation supplied to its field or input circuit It. his enerato may bereplaced by a direct current machine of the armature-reaction excitedtype, such, for example, as that disclosed and claimed in Patent No.2,227,992, E. F. W. Alexanderson and M. A. Edwards, January "I, 1941,assigned to the assignee of this application. Furthermore, an electronicamplifier may be employed in lieu of the dynamo-electric type, ifdesired.

The pilot exciters driven by the dynamometer may or may not be cradledwith the dynamometer depending upon the required size thereof. Whenthese pilot exciters are of such small size in comparison to the size ofthe dynamometer that the torque required to drive them is negligiblethese units need not be cradled. Hence, by the employment of anamplifier for the output of exciter generator armature l5, small pilotexciter generators may be used and thereby avoid the expense andinconvenience of mounting the exciter generators in a manner toascertain their load requirements.

The excitation system includes a field exciting winding 20 for the pilotexciter generator armature' |4 arranged to be energized by a constantvoltage source of electrical power supply 2| by connecting the fieldexciting winding 20 across a potentiometer 22 and in series with acontrol or variable resistor 23. This results in the generation of avoltage by the exciter armature l4 which is substantially proportionalto the speed of the dynamometer l3. This first power speed voltage isadapted to energize a field exciting winding 24 by closing a switch 25to excite the pilot exciter armature l5. This pilot exciter also isprovided with a field exciting winding 26 arranged to be energized bythe constant voltage source of electrical power supply 2| by connectingit across a potentiometer 21 connected to the source of power 2|. Whenthe switch 25 is open and the field exciting winding 24 deenergized, thepilot exciter generator armature generates avoltage directlyproportional to its speed due to the excitation of the field excitingwinding 25. When the switch 25 is closed, the armature l5 generates avoltage proportional to the square of its speed due to the excitation ofthe field exciting winding 24. The field exciting winding 24 and 26 areboth adapted to produce magnetic fluxes in the same relative directions.

The amplifier exciter field exciting winding I8 is connected in serieswith a Vernier control rheostat 28 and across a potentiometer 29connected to a switch 30 arranged to connect the potentiometer 29 acrosseither the source of supply 2| or the pilot exciter generator armatureIS.

The dynamometer field producing means comprises an auxiliary fieldexciting winding 3| in addition to the winding l6. These windings areconnected to produce magnetic fluxes in the dynamometer which are in thesame relative direction. The field winding 3| is connected to theconstant voltage source 2| through a potentiometer 32 and a Vernierrheostat 33 for supplying a controllable constant component ofexcitation when the dynamometer excitation is being obtained from twoindependent voltage sources.

In order more fully to explain the operation and manner of adjustment ofthe system, Fig. 2 has been presented to show typical curves of theexcitation supplied to the dynamometer field winding I6 obtained with myimproved excitation system. These curves have been drawn to show thegeneral relationships obtainable between the dynamometer excitation andthe speed. The curve 0A represents the dynamometer excitationcharacteristic which is obtained by the use of only the constant voltagecomponent of excitation supplied to the pilot exciter field excitingwinding 26. For such a condition 01' operation the excitation of thedynamometer is caused to vary linearly with the speed thereby producinga corresponding change in the dynamometer torque. The rate of rise ofexcitation with speed may be controlled by the potentiometer 21. Thecurve OB-represents the type of excitation characteristic obtainablewithout any fixed component of excitation applied to the field of thispilot exciter. This may be accomplished by adjusting the variablepotentiometer 21 so that the voltage obtained from the source of supply2| is zero. In this case the dynamometer excitation is varied inaccordance with the square of the speed to produce corresponding changesin the dynamometer torque. The characteristic 00 represents the combinedexcitation characteristic obtainable when both of the excitation sourcesincluding the field windings 24 and 26 are in operation. It is clearthat, with the field adjustting elements of the pilot exciters set to agiven position, the magnitude of the energizing current supplied to thedynamometer field exciting winding It may be adjusted by means of therheostats 28 and 29. By proper adjustment of the exciter generator fieldcontrol elements, the relative magnitudes or proportions of the twoexcitation components supplied to the dynamometer for a given speed orspeeds may be altered as desired to impose horsepower loads on theengine which vary automatically as a function of speed in the desiredmanner. For example, by varying the potentiometer 22 to reduce thevoltage applied to the field exciting winding 20 the rate of rise or themagnitude of the voltage component for exciting the dynamometer fieldwhich varies as the square of the speed is correspondingly varied.

In describing the operation of the arrangement, the switch 30 wasassumed to be thrown to the left to connect the dynamometer fieldexciting winding IS with the pilot exciter generator armature l5 throughthe amplifier i1 and I8 for automatic operation. At times it may bedesirable to use manual control and eliminate the effect of theautomatic excitation completely, that is, to secure excitation for thedynamometer which is independent of speed changes. For such operationthe switch 30 is thrown to the right to connect the input field circuitll! of the amplifier to the constant voltage direct current source ofsupply 2|, and in this way the system operates with conventionalconstant excitation which can be adjusted by the potentiometer 23 andvemier 28 to obtain the desired load. All or a portion of this constantexcitation may also be provided by means of the dynamometer fieldexciting winding 3|.

When it is desired to operate the system by supplying a constantcomponent of excitation to the dynamometer in conjunction with thecomponent or components which are functionally related to the speed, theswitch 30 is thrown to the left and the constant component of excitationis supplied to the field exciting winding 3| through the rheostat 32 insuch a manner that both voltages cause magnetic fiuxes to be produced inthe dynamometer in the same relative direction. This connection alsoserves the additional purpose of permitting maximum excitation at anyspeed down to zero on the dynamometer thereby permitting maximumavailable torque to be obtained on the dynamometer even at low speeds.

I have thus, provided an improved excitation system which is capable ofdelivering a voltage which is independent of speed for exciting thedynamometer field. I have also provided an arrangement whereby thedynamometer excitation maybe varied directly as the speed therebyproducing a modified shape in the horsepower-speed characteristic of thedynamometer. Further, I may obtain a dynamometer excitationcharacteristic which is approximately proportional to the square of thespeed in order to produce a change in the horsepower-speedcharacteristic such that the horsepower absorption increases at a fasterrate with respect to speed. Also by combining in additive relation theexcitation component for the pilot exciter armature ll which isindependent of the speed with the component of excitation which varieswith the speed, the total excitation supplied to the dynamometer may bemade automatically to vary in accordance with the first power of thespeed and over a range including the second power with the result thatthe horsepower absorption of the dynamometer as a function of speed maybe made to assume intermediate values.

I have also provided means whereby a constant component 01 excitationmay be supplied simultaneously to the dynamometer with the component orcomponents which are functionally related to the speed. This latterarrangement contributes toward still greater flexibility in theoperation from the standpoint of making it possible to produceadditional changes in the shape or slope of the total dynamometerexcitation characteristic. It also renders it possible to obtain maximumexcitation on the dynamometer at low speeds with relatively smallexciters, and at the same time is eflective to provide a stabilizingaction to prevent hunting or overspeeding by producing a pronouncedincrease in the dynamometer torque with increases in speed in thosecases where the dynamometer would have a fiat or nearly uniformspeed-torque characteristic over a large part of its speed range if theexcitation were held at a constant value.

The apparatus is thus adapted for producing in the laboratory varioustorque-speed and horsepower-speed relationships for simulating difierenttypes of loads so that operating characteristics similar to that foundin actual practice from the standpoint of stability and control may beobtained. Th apparatus is particularly useful in those cases where theexcitation and torque of the dynamometer are not related in a simplemanner. In other words, in order to obtain an absorption torque, forexample, which varies as the square of the speed, it may be necessary toincrease the field excitation at a difierent rate. Also, due todifierences in various machine designs, this rate or the relativecurvature of the total required dynamometer excitation curve changes fordifferent machines. This diflerence in excitation rate is readilyobtainable by changing the proportions or relative magnitudes of thevarious excitation components.

While I have illustrated and described a particular embodiment of myinvention, modifications thereof will occur to those skilled in the art.I

desire it to be understood, therefore, that my invention is not to belimited to the particular arrangement disclosed, and I intend in theappended claims to cover all modifications which do not depart from thespirit and scope of my invention.

Letters Patent of the United States is:

1. An electrical testing system including an electric dynamometer forloading the prime mover to be tested, said dynamometer 'having first andsecond field exciting windings for controlling the speed-torquecharacteristics thereof, a first exciter generator having a fieldexciting winding and an armature member adapted to be driven at a speedproportional to the speed of said dynamometer, means for energizing saidfirst field exciting winding of said dynamometer in accordance with thevoltage variations in the armature of said first exciter generator, asecond exciter generator having field producing means and an armatureadapted to be driven at a speed proportional to the speed or saiddynamometer, a substantially constant voltage source of electrical powersupply, means for connecting said field exciting winding of said firstexciter generator for energization thereof in accordance with the volt-88c variations in said armature of said second exciter generator and forproviding excitation in the same direction as said first field excitingwinding of said first exciter, and means for energizing said secondfield exciting winding of said dynamometer from sai constant voltagesource of electrical power supply for providing excitation in the samedirection as said dynamometer first field exciting winding.

2. A prime mover electrical testing system including an electricdynamometer for loading the prime mover to be tested, said dynamometerhaving first and second field exciting windings for controlling thespeed-torque characteristics thereof. a firstexciter generator havingfirst and second field exciting windings and an armature member adaptedto be driven at a speed proportional to the speed of said dynamometer,means including an amplifier for energizing said first field excitingwinding of said dynamometer in accordance with the voltage variations inthe armature of said first exciter generator, 8. second excitergenerator having field producing means and an armature adapted to bedriven at a speed proportional to the speed of said dynamometer, asubstantially constant voltage source of electrical power supply, meansfor connecting said first field exciting winding of said first excitergenerator for energization from said constant voltage source ofelectrical power supply, means for connecting said second field excitingwinding of said first exciter generator for energization thereof inaccordance with the voltage variations in said armature of said secondexciter generator and for providing excitation in the same direction assaid first field exciting winding of said first exciter, and means forenergizing said second field exciting winding of said dynamometer fromsaid constant voltage source of electrical power supply for providingexcitation in the same direction as said dynamometer first fieldexciting winding 3. In combination in a device for testing prime movers,an electric dynamometer for loading the prime mover to be tested, saiddynamometer having first and second field exciting windings forcontrolling the speed-torque characteristics thereof, a first excitergenerator having first and second field exciting windings and anarmature member arranged to be driven at a speed proportional to thespeed of said dynamometer, means for energizing said first fieldexciting winding of said dynamometer in accordance with the voltagevariations in said armature of said first exciter generator, 5, secondexciter generator having a substantially constant'field producing meansand an armature arranged to be driven at a speed proportional to thespeed of said dynamometer, a substantially constant voltage source ofelectrical power supply, means for connecting said first field excitingwinding of said first excitet generator for energization from saidconstant voltage source of electrical power supply, means for connectingsaid second field exciting winding 10 oi said first exciter generatorfor energization thereof in accordance with the voltage variations insaid armature of said second exciter generator and for providingexcitation in the same direction 5 as said first field exciting windingof said first exciter, and means for energizing said second fieldexciting winding of said dynamometer from said constant voltage sourceof electrical power pp y.

RICHARD H. KAUFMANN.

